Thermoformed articles (vacuum formings, pressure air formings, and matched-die moldings) made from polyolefin resin sheets containing an inorganic filler are used as various food containers or as industrial parts (see, e.g., JP-A-52-63283 and JP-B-3-20331, the term "JP-A" as used herein means an "unexamined published Japanese patent application", and the term "JP-B" as used herein means an "examined published Japanese patent application"). These thermoformed articles have advantages such as high rigidity, high heat resistance, and a low heat of combustion but have the disadvantage of being heavy due to the inorganic filler (the density ranges from 1.1 to 1.5 g/cm.sup.3). Besides the heaviness of these articles, inorganic filler containing polyolefin resin sheets exhibit poor ink receptivity and/or unclear, poor printability when subjected to offset printing.
Synthetic paper having excellent offset printability and gravure printability include laminated resin sheets comprising a biaxially stretched finely porous thermoplastic resin film as a base layer having laminated thereon a uniaxially stretched thermoplastic resin film containing an inorganic fine powder as a paper-like layer is known and disclosed in, e.g., JP-B-46-40794, U.S. Pat. No. 4,318,950, JP-B-50-29738, JP-A-54-74842, JP-A-56-141339, and U.S. Pat. No. 4,420,530.
Synthetic paper with opaqueness and a pearly luster attributed to light scattering due to voids therein is also known, comprising a biaxially stretched film of a thermoplastic resin containing an inorganic filler, e.g., calcium carbonate, or a blend of a thermoplastic resin and an incompatible resin, e.g., polyamide, polyethylene terephthalate, or polyoxymethylene (see JP-A-61-157547, U.S. Pat. No. 4,191,719, JP-B-60-37793, and U.S. Pat. No. 3,773,608). A void formation technique utilizing the crystal morphology inherent in polypropylene is also known (see JP-B-55-40411).
When conventional synthetic papers like those described above are used for applications demanding high rigidity (coin cases, signboards to be set up, or hanging signs) a plurality of sheets of the synthetic paper each 30 to 300 .mu.m thick must be bonded together to obtain the necessary thickness, making the resulting laminated article extremely expensive. Further, since each synthetic paper sheet to be laminated has already been oriented, the thick and rigid laminated sheet undergoes shrinkage on heating during thermoforming and often slips out of the sheet feeding chain. Where the sheet is clamped so as not to slip out, the sheet itself tends to break. If thermoforming of the thick laminated sheet is effected with heating at a relatively low temperature so as to prevent thermal shrinkage, the draw of the sheet is insufficient for obtaining a shaped article.